Electrostatically focused traveling wave tube



129. .1 58 Btmzm 2,845,571

. ELEGTROSTATICALLY FOCUSED TRAVELING WAVE "TUBE Filed April 17. 1953 b5?:I:22111211112117.1222:1112211222211 G@EEBFBBQBBB -mmmu-armmb- FIG. I

FIG. 3

INVENTOR.

BENJAMIN KAZAN 4H0 ray different potential. are formed actingtoconcentrate the electron beam;

the invention Will be described in p V I Patented July 29, 19 58 1 A i ia invention may, however, have application in'a wide vari- 2.s4s,57.1ety of fields. I

' HELECTROSTATICALLY FOCUSED TRAVELING WAVE TUBE Benjamin K'aian,Princeton, N. J., assignor to the United States of America asrepresented by the Secretary of the Army (Granted underTitle 35, U.S..Cde 1952 sec. 266) The invention described herein may be manufacturedand used by or for the Government for governmental purposes without thepayment, of any royalty thereon.

This invention relates to that type of'radio frequency amplifier knownas a traveling wave tube in which the amplifying ability of the tuberesults from the transfer of'power to the traveling wave from anelectron beam and the invention is particularly directed to a manner offorming the electron beam. 7 V

In tubes of the type suggested a special problem arises in providing anelectron'be'am which will remain under control for the purpose intendedthroughout the relatively long path of travel of the electrons. It hasbeen common practice to provide an electromagnetic field to control thebeam. Such a field is created by an elongated hollow cylindrical coil ofa length to embrace 'thelengtli of the beam and Within'which the tubeitself is received. This construction is of necessity relatively largean'd'heavy and is very wasteful of power which must be supplied to thecoil.

metallic electrodes arranged in' alignment and having aligned aperturesthrough which the'ielect-ron beam is axially directedand dielectricrings between the metal rings. 1 a

In operation direct current potentials are; applied to the metallicelectrodes in a pattern to suit the particular requirements of a'givenapplication. A desirable arrangement would be to divide the metallicmembers into groups in su'cha way-that successive electrodes have'a Thusa series ofelectrostatic lenses Preferred forms of detail hereinafter. I

Itis a primary object ofthe invention to provide'a simplified and moreefiicient traveling wave tube.

A further objectof the invention is toprovide a traveling wave tubehaving an electron beam focusing means characterized by greatversatility-of control and particularly by its ability to controlsubdivided portions, thereof.

A further object of the invention is to provideina traveling wave tubean electron beamv focusing device which requires only a minimumof'power-forits operation. a I Other objects and features of theinvention will more fully appear fromthe following description taken inconnection with the. accompanying drawings in which Fig. 1 is adiagrammatic illustration of a -preferred embodiment of'the invention.

Fig. 2 illustrates a modified formof the invention. Fig. 3 is across-sectional view taken on line 3-3 F g.1. v The invention will bedescribed in connectionwith a traveling wave amplifier tube. The,principlesjoffthe The elements (of the invention are inclosed within anevacuated envelope 4. The beam of electronsmay be supplied in anysuitable manner such as by a conventional electron gun having a cathode5, an accelerator anode 6 and a collector 7.. The gun issupplied withsuitable power from sources not shown.

To provide efiicient operation of the device the electron beam must bekept under the influence of a concentrating or focusing element. Thepresent invention provides such. an element which possesses qualitieswhich are novel and which contribute to the overall operating efliciencyand versatility. of the device.

In place of the usual electromagnetic coil, the focusing device isconstructed to function upon theelectrostatic principle and is composedof a plurality of electrodes 8 spaced apart and arranged symmetricallywith respect to'the axis of the electron beam. The discs are held inplace by spacing rings 9 of dielectric material situated between theadjacent electrodes 8. I The succession of metallic electrodes8 arrangedas they are provides an ideal means for controlling the dispersion ofthe beam since it is possible not only'to apply any desired potential toeach one but it is also possible to provide diiferent potentials tosuccessive individual electrodes or groups of electrodes.

In the drawings a suggested arrangement is tov interconnect every otherelectrode to a common .lead wire 10' and, the remaining groups ofelectrodes to a separate common lead Wire 11. The voltage applied toeach group may be so chosen that in elfect' the successive groups ofelectrodes constitute a series of electroniclenses of the requiredstrength to confine the electrons to..a path along the tube axis.

Along with the above arrangement of electrostatic lenses other mattersmust'be considered. It Will he understood that provision must be madeforsynchronizing the phase velocity of the radio frequency wave with thevelocity of the electron beam which must. be correct. to sustain theamplifyingability of the .tube as in a conventional traveling wave tube.

In all traveling wave tubes there must be some means for slowing thetraveling wave such as a heliX of conductive material which is widelyused in conventional tubes for this purpose. In the present invention,however, the wave slowing means is not determined solely by theelectrodes 8 butthe degree of retardation is determined by thedielectric constant of the dielectric used for the spacing rings 9 andthe dimensions of the electrodes 8 and insulator rings 9. Thecombination of insulator rings and electrodes together comprise a waveloading or wave slowing structure.

In orderto prevent the successive electrodes 8 from being held at acommon R.-F. potential' by the leads from the battery, resistors areshown inserted between each electrode and the battery so that theelectrodes will have high R.-F. impedances to each other through thebattery supply. Instead of resistors, other, high impedance R.-F.elements may be substituted. I p

A tube embodying the invention may therefore be designed, by choosingthe proper: dielectric for-the spacer rings 9 and determining thedimensions of the-structure which will cause the-tube to function withinthe specifications desired. Then by choosing the correct potential to beapplied to the cathode with respect to thegroups of,

electrodes 8 connected respectively to wires 10,-and 11, the

electron beam will have the correct average velocity to be synchronizedwith the: travelingwaveon the wave slowing structure. As above stated,the potentialson the groups of electrodes 8 may also be so chosen thattheir dilference.

will be a value which satisfies the condition wherein successive pairsof electrodes 8 act as electrostatic lenses to concentrate the electronbeam to the required degree.

It will thus be apparent that all conditions for amplification of theWave are provided and the tube may be efficiently operated without anexternal cumbersome electromagnetic coil to concentrate the electronbeam.

The power to be amplified may be introduced in any suitable manner. Amethod for accomplishing this is shown in Fig. 1 wherein the input endof the tube is provided with an opening within which is sealed a sectionof waveguide 12 of standard dimensions which is provided with a flangefor connection to a waveguide system conducting power to be amplified. Asimilar section of waveguide 13 may be provided at the output end of thetube to feed amplified power to a subsequent utilization circuit ordevice.

The invention may embody other structural forms such as that shown inFig. 2 wherein the peripheral edge of the aperture in each of theelectrodes 8 is made relatively wide to form a short section of tube 14through which the electron beam passes. By thus modifying the structurea stronger focusing effect on the beam may be realized.

What is claimed is:

1. A traveling Wave amplifier tube circuit comprising an exhaustedenvelope to enclose the elements thereof, combined electrostaticfocusing and wave retarding means including a plurality of spacedmetallic electrodes arranged in alignment within said envelope, aplurality of di electric elements alternately arranged with saidelectrodes, acting to insulate successive electrodes and to act as aradio frequency wave slowing means, means to supply and direct a beam ofelectrons along said electrodes, a source of direct-current potentialseparately connected to each of said electrodes to electrostaticallyconverge said electron beam, and means having a high impedance toradio-frequency currents connected between said electrodes and saidsource of potential, and means to feed power to be amplified to theinput of the tube and to conduct the amplified power therefrom.

2. A traveling wave amplifier tube circuit comprising an exhaustedenvelope, a combined electrostatic focusing and wave retarding meansincluding a plurality of spaced metallic electrodes arranged inalignment within the envelope, a plurality of dielectric elementsalternately arranged with said electrodes, means to supply and direct anelectron beam along said electrodes and dielectric elements, a source ofpotential of one polarity separately connected to each of one group ofsaid electrodes and a potential source having an opposite polarityseparately connected to each one of another group of said electrodes toprovide a series of electrostatic lenses for converging said electronbeam, high impedance means connected between said electrodes and saidpotential source, and means to feed power to the tube and to conductamplified power therefrom.

3. A traveling wave amplifier tube circuit comprising an exhaustedenvelope, a combined electrostatic focusing and wave retarding meansincluding a plurality of spaced metallic electrodes within the envelopehaving aligned apertures, means to supply and direct a beam of electronsalong said electrodes, a plurality of annular shaped dielectric elementsalternately arranged with said electrodes presenting a radio frequencywave slowing channel for the passage of power therethru, a steppedsource of direct-current potential separately connected to each of saidelectrodes whereby adjacent electrodes may have different potentialvalues to create a series of electrostatic lenses for concentrating theelectron beam, radio-frequency isolating means connected betwen saidelectrodes and said source of electrical potential, and means to feedradio frequency power to and conduct it from the tube.

4. A traveling wave amplifier tube circuit comprising an exhaustedenvelope, a plurality of aligned metallic electrodes spaced apart withinsaid envelope, means to supply and direct a beam of electrons along saidelectrodes, a stepped direct-current potential source separatelyconnected to each of said electrodes to supply successive electrodeswith different potentials whereby a series of electrostatic lenses areformed to concentrate said electron beam, high impedance means connectedbetween electrodes and said potential source, and a channel structure ofdielectric attenuating material extending along said electron beamacting as a radio frequency wave slowing and synchronizing means, saidchannel structure comprising a plurality of dielectric elementsalternating with said electrodes.

5. A traveling wave amplifier tube circuit comprising an evacuatedenvelope, means to supply and direct a beam of electrons along apredetermined path, a plurality of spaced metallic electrodes extendingin line along said path, a wave loading structure of dielectric materialextending along said path, said structure comprising a plurality ofdielectric elements alternating with said electrodes, a steppeddirect-current potential source separately connected to each of saidelectrodes and having an average value calculated to synchronize theelectron velocity with the phase velocity of the loaded wave at theoperating frequency and wherein different values of potential areapplied to successive electrodes to form a series of electrostaticlenses acting to concentrate said electron beam, and radio-frequencyisolating means connected between said electrodes and said potentialsource.

6. A traveling wave amplifier tube circuit comprising an exhaustedenvelope, a plurality of aligned spaced electrodes in said envelope,means to supply and direct a beam of electrons along said electrodes, aplurality of spaced aligned metallic plate-like electrodes in saidenvelope, a wave loading dielectric structure having elementsalternately arranged with said electrodes acting to support and insulatethem in spaced relation, a stepped potential source including waveisolating means connected to each of said electrodes separately andhaving an average value to synchronize the phase velocity of the loadedwave with the electron velocity at the operating frequency and whereindiflerent values of potential are applied to successive electrodes toform a series of electrostatic lenses acting to concentrate the electronbeam.

7. A traveling wave amplifier tube circuit comprising an exhaustedenvelope, a plurality of spaced electrodes in said envelope, eachelectrode having short tubular axially aligned portions forming an openchannel, means for sup plying and directing a beam of electrons throughsaid channel, a wave loading structure of dielectric material alsoextending along said electron beam, said structure comprising aplurality of dielectric elements alternating with said electrodes astepped source of potential including wave isolating means connected toeach of said electrodes separately and having an average value tosynchronize the electron velocity to that of the traveling wave at theoperating frequency and to supply successive electrodes with difierentpotentials to form a series of electrostatic lenses, operable toconcentrate the electron beam.

8. A traveling wave amplifier comprising means to generate an electronbeam, means to propagate radio frequency wave energy along said beam,and a combined wave retarding and beam focusing structure comprising aplurality of substantially noninductive electrostatic wherein saidelements have aligned apertures through which said beam is directed.

10. A traveling wave amplifier comprising means to generate an electronbeam, means to propagate radio frequency wave energy along said beam,and a combined wave retarding and beam focusing structure compris- 1 inga plurality of electrostatic focusing elements having I 11. A travelingwave amplifier as set forth in claim 8, wherein said focusing elementsare insulated from each other.

References Cited in the file of this patent UNITED STATES PATENTS2,313,018 Krause Mar. 2, 1943 2,533,790 Grivet Dec. 12, 1950 2,654,047Clavier Sept. 29, 1953 2,660,689 Touraton et a1 Nov. 24, 1953 2,661,441Mueller Dec. 1, 1953 2,672,572 Tiley Mar. 16, 1954 2,725,499

Field Nov. 29, 1955

